1. Technical Field
The present invention relates to digital video signal encoding for transmission and, more particularly, to an adaptive encoding scheme that is independent of the video data format, the nature and bandwidth of the transmission medium, and the bit transmission rate.
2. Discussion of the Prior Art
In certain types of digital video signal transmission systems, the parameters of the digital video signal that is received at a particular location are subject to change. For example, in aerial surveillance systems, video cameras on one or more aircraft may require changes in an operating parameter such as image resolution as the flight conditions change. Typically, the images are digitally encoded for transmission and transmitted by a microwave transmitter to a tracking antenna where the received signal is synchronized and decoded. In some cases the digitally encoded video signals are encrypted before transmission and then decrypted when received. Clearly, the encoder on the aircraft and the decoder at the receiver must be synchronized (i.e., have the same settings) in order to be compatible. If camera resolution is changed, for example, the encoder setting is changed, thereby requiring that the decoder setting be changed. Often, the decoder is at an unmanned location, thereby rendering decoder adjustment inconvenient, if not impossible. Even where personnel are present at the decoder, two people at different locations are required to effect the necessary changes at the encoder and decoder. These people must be in voice contact which, under some circumstances, is not feasible.
In addition to video parameter changes from a single camera, multiple cameras may provide transmitted video signals to the same receiver operated in a manner to selectively receive those signals. Systems using such multiple cameras might be, for example, aircraft surveillance systems, road traffic monitoring systems, etc. The cameras may have different coded video signal formats and parameters, and may transmit their digital video signals over substantially any transmission medium (e.g., microwave, telephone line, fiber optic systems, etc.), thereby requiring the decoder at the receiver to be adjusted for each of the received signals. Automatic decoder operation is virtually impossible without highly complex and space-consuming equipment.
It is desirable to provide a video image transmission system wherein the decoder at a receiver automatically adapts to each received digital video signal irrespective of the video signal format and parameters, the type of transmission medium and the transmission bit rate.